Re: [Qemu-devel] [PATCH v7 03/14] replay: exception replay fix

[Paolo Bonzini]

On 25/01/2017 12:33, Pavel Dovgalyuk wrote:
>> From: Paolo Bonzini [mailto:address@hidden
>> On 25/01/2017 12:12, Pavel Dovgalyuk wrote:
>>>> From: Paolo Bonzini [mailto:address@hidden
>>>> On 24/01/2017 08:17, Pavel Dovgalyuk wrote:
>>>>> @@ -451,6 +451,10 @@ static inline bool cpu_handle_exception(CPUState 
>>>>> *cpu, int *ret)
>>>>>  #ifndef CONFIG_USER_ONLY
>>>>>      } else if (replay_has_exception()
>>>>>                 && cpu->icount_decr.u16.low + cpu->icount_extra == 0) {
>>>>> +        /* Break the execution loop in case of running out of TB cache.
>>>>> +           This is needed to make flushing of the TB cache, because
>>>>> +           real flush is queued to be executed outside the cpu loop. */
>>>>> +        cpu->exception_index = EXCP_INTERRUPT;
>>>>>          /* try to cause an exception pending in the log */
>>>>>          cpu_exec_nocache(cpu, 1, tb_find(cpu, NULL, 0), true);
>>>>>          *ret = -1;
>>>>
>>>> Why is replay_has_exception() related to be running out of TB cache?
>>>
>>> It doesn't.
>>> Calling tb_find when there is not space in cache causes tb_flush and 
>>> cpu_loop_exit.
>>> But execution loop will continue, because there is no reason to break it
>>> (like setting exception_index).
>>
>> What about setting cpu->exit_request?  queue_work_on_cpu calls
>> qemu_cpu_kick.
> 
> cpu->exit_request does not checked in this loop.
> We have to add this checking somewhere then?

It's checked by cpu_handle_interrupt.  Are you not reaching
cpu_handle_interrupt then?  Why?

Or perhaps cpu_handle_interrupt should not be testing cpu->exit_request,
but cpu->exception_index != -1 (and cpu_exit can cmpxchg
cpu->exception_index from -1 to EXCP_INTERRUPT)?

Again, it's hard to follow without knowing the invariants. :(

Paolo